The false widow spider hasn't got a fatal bite. The effect of its bite is akin to that of a wasp sting; this according to the expert from the Natural History Museum, on the BBC.. Some people are unlucky enough to react badly to wasp stings, and the same is true of spider bites here, but that still doesn't make our false widow 'deadly'. It's not like its relative the widow spider, which is not found living in Britain, but which is fully capable of killing a human.
Spiders living in our houses like being in our houses; putting them outside is definitely not to their liking. If they survive, they'll just come back in again. None of them are a danger to health and none are dangerous.Too many? Depends what you mean by that. The population is self controlling; if there's enough food to sustain a population, that's the greatest population you'll get. You probably have the maximum that circumstances allow: 'house spiders' do tend to attack other spiders in their territory , making some difference.